I have to admit, when Zed was first working on Mauls legs when he was unconscious, he was a little flustered. He felt a bit awkward, and he didn't really know why, after being so disconnected from his emotions for so long, and especially since he knows who this guy is and knows he means trouble. But he wasn't doing anything. He looked peaceful for someone he heard so many destructive things about. But he also felt it weird to be gazing at this unconscious guy for so long, so he tried his best not to look at his face very much. And again, there was all that on top of the fear that he'd wake up and expose his then secret of being a fallen jedi.
And then, when helping him recover after the death of his mom, watching him again, it felt even more awkward and flustering, because there was no more fear left, and he didn't understand that. And this time, he would be looking at him more often, when he was needed, just to make sure he was still alive. his feelings were confusing.
And even then the third time(yes this happens to him a lot) In my healing AU, where maul returns to Zed, collapsing in his arms. He's again conflicted, as he's still hurt by maul, and wary that he'd be used again. But seeing how they're so force bonded now, he's in tune with his emotions, and he can feel all the regret, and all the love, and this time, its easier to start gazing at him more lovingly after a while. I think Maul can tell, and I think this time, as opposed to others, it makes him feel safe.
And Maul isn't a stranger to this either, becuase when Zed found Maul after order 66, Maul took care of him until the others regrouped. He had let himself fall in love then too, taking care of him, and was a bit flustered by cleaning his wounds. He would glance at Zed with confliction in his heart, confliction he would soon give into.
Afterwards he's just very watchful and protective around Zed, and will even do so in the healing AU, in spite of his increased phsycial limitations.